The invention relates to a gas/liquid contacting apparatus comprising a column having its interior provided with perforated gas/liquid contacting trays for effecting intimate contact between liquid and gas flowing counter-currently through said column.
More in particular, the present invention relates to a gas/liquid contacting apparatus comprising a normally vertically extending column having a plurality of substantially horizontal trays arranged one above the other in the column, each tray having a plurality of apertures for the passage of ascending gas and at least one discharge device for descending liquid, the discharge devices being open at their upper ends and extending at least partly below the relevant trays, the parts of the discharge devices extending below the relevant trays being provided with liquid discharge openings. In operation, liquid is introduced at the top of the column and the gas phase at the bottom of the column, so that the difference in density constitutes a driving force causing the liquid and the gas to flow through the column. The trays define a series of contacting zones wherein the liquid and the gas are brought together in intimate admixture for contacting.
The term "gas" as used throughout this specification and the claims is to be understood to include vapor.
Apparatuses of the above-mentioned type may be suitably used for carrying out processes like distillation, absorption and stripping. Examples of trays which may be applied in such an apparatus are grid trays, sieve plate trays which are formed of plates that are punched or otherwise fabricated to have circular or other apertures for gas passage, and valve trays which are sieve trays provided with valves which are displaceably arranged in the tray-apertures. Liquid is transferred from one tray level to another via liquid discharge means, hereinafter called downcomers, mounted in openings of the trays. The liquid discharge openings in the lower parts of the downcomers are so arranged that these openings are properly sealed against upward flow of gas during operation of the column. The downcomers normally extend partly above the relevant trays to establish a liquid level on the trays in the contacting zones.
If the contacting trays are to accomplish their mass transfer function efficiently they should be supplied with de-aerated liquid from the tray above in order to minimize vapor back-mixing between the contacting zones. The downcomers in which the liquid from the contacting zones is collected should allow the separation of the liquid and gas phases within them.
The maximum capacity of a column provided with contacting trays having liquid downcomers is reached when either the dispersion of liquid and gas fills the whole space between adjacent trays, resulting in flooding of the column, or when the pressure drop over the trays can no longer be balanced by the liquid holdup in the downcomers, also resulting in flooding of the column.
Within the oil and gas industries there are a number of operations involving counter-current gas/liquid contacting under conditions of high gas density and low interfacial tension between the liquid phase and the gas phase, for example, fractionation near the critical region. These have traditionally been a source of concern with regard to both capacity and operational stability. Over a wide range of conditions it has been found that for a given liquid flow rate, the maximum possible gas loading through a given tray is determined from a constant maximum load factor. High pressure operation, however, may cause a sharp decrease of the load factor at maximum capacity, due to a decrease of the density differences between the fluid phases.
The object of the invention is to provide a gas/liquid contacting apparatus which is suitable for high pressure operation in that the adverse influence of high pressure on the maximum capacity of the apparatus is eliminated or at least minimized.